Python retains metadata methods for decorated functions

This article mainly introduces in detail how python retains metadata for decorated functions. I hope it can help you.

Case:

The function object stores some function metadata, such as:

f.__name__ Function name

                                                                                                                                                                                                               f.__defaults__                                                                                                                                                      

After using the decorator, when accessing the above properties in the decorator, what we see is the metadata of the decorator function

Requirements:

Implemented in the decorator function, retaining the metadata of the decorated function

How to implement this?

                                                                                                                                                                implemented through the wraps and update_wrapper methods in functools, each of which can be implemented independently

#!/usr/bin/python3
 
import time
from functools import (wraps, update_wrapper, WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES)
 
 
def count_time(func):
  """
  给目标函数加上计算运行时间统计
  """
  # 这个装上器和update_wrapper一样，默认参数WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES
  @wraps(func)
  def wrapper(*args, **kwargs):
    start_time = time.time()
     
    # 定义result接收函数返回值，并且在装饰函数最后返回回去
    resutl = func(*args, **kwargs)
    print('运行时间：', time.time()-start_time)
    return resutl
   
  # 其中默认参数 WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES
  # update_wrapper(wrapper, func)
  return wrapper
 
 
@count_time
def add(num=100):
  """
  计算 0~num 累加值，默认num=100
  """
  time.sleep(1)
  return sum([x for x in range(num+1)])
 
if __name__ == '__main__':
  print('函数名：', add.__name__)
  print('属性字典：', add.__dict__)
  print('函数默认参数：', add.__defaults__)
  print('函数所在模块：', add.__module__)
  print('函数文档：', add.__doc__)
   
  # 打印两个默认参数
  print(WRAPPER_ASSIGNMENTS, WRAPPER_UPDATES)
  result = add()
  print(result)

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